1. Field of the Invention
The present invention relates to a solid electrolytic capacitor used in a variety of electronic equipment and a manufacturing method thereof.
2. Background Art
FIG. 12 is a sectional view of a structure of a conventional solid electrolytic capacitor. FIG. 13 is a perspective view of a capacitor element used in the solid electrolytic capacitor. FIG. 14 is a perspective view showing a state in which the capacitor elements are laminated on anode/cathode lead frames. FIG. 15 is a sectional view of an essential part of a state in which an anode section used in the conventional solid electrolytic capacitor is joined to the anode lead frame.
In capacitor element 11, as shown in FIG. 15, dielectric oxide film layer (it is hereinafter called film layer) 11B is formed on a surface of anode body 11A composed of aluminum foil, namely a valve action metal. Insulating resist part 12 separates anode section 13 from cathode section 14, and a solid electrolyte layer and a cathode layer (none of these are shown) are sequentially laminated on the surface of cathode section 14. Connecting parts 16A are formed by partially and vertically bending a flat part of cathode lead frame 16. Two sets of a plurality of capacitor elements 11 are laminated so that anode sections 13 are disposed on each of front and back surfaces of anode lead frame 15 and cathode sections 14 are disposed on each of front and back surfaces of cathode lead frame 16. Respective anode sections 13 of capacitor elements 11 are integrally joined to anode lead frame 15 by resistance welding. Respective cathode sections 14 are integrally joined to connecting parts 16A formed on cathode lead frame 16 via a conductive silver paste (not shown). The connecting parts 16A are positioned on the side surfaces of capacitor element 11 in the thickness direction. Insulating packaging resin 17 integrally covers the plurality of capacitor elements 11 so that anode lead frame 15 and cathode lead frame 16 are partially exposed from the outer surfaces of packaging resin 17. Anode lead frame 15 and cathode lead frame 16 extending out of packaging resin 17 are folded along packaging resin 17 to form respective external terminals. A surface-mount-type solid electrolytic capacitor is thus provided.
The conventional solid electrolytic capacitor has a problem in which welding can be extremely difficult when each of anode sections 13 of capacitor elements 11 is integrally joined to anode lead frame 15 by resistance welding. That is because film layer 11B is formed on the surface of anode section 13. This phenomenon is described with reference to FIG. 15. Film layer 11B is formed on the surface of anode body 11A in anode section 13 of capacitor element 11. Therefore, when anode section 13 is joined to anode lead frame 15 made of a material other than the aluminum forming capacitor element 11 by resistance welding using welding electrode 18, film layer 11B works as a high resistance to disturb flowing of the welding current. Only a part or no part of anode body 11A is therefore welded onto anode lead frame 15. Therefore, not only a defect due to insufficient welding strength but also increase and variation of equivalent series resistance (ESR) occurs.
For addressing the foregoing problems, a method such as increase of the welding currents or joining by laser welding is considered. However, in welding by this method, molten aluminum can extend to an exposed place of anode body 11 A such as a cut surface of anode section 13, or can be splashed. As a result, the new following problems occur: damage of the outward appearance, reduction in air tightness because of the a decrease of the thickness of packaging resin 17 by an amount corresponding to the extending aluminum, and occurrence of a short circuit.